This invention relates to nozzles for discharging liquid commodities and relieving excess pressure from liquid transporting vehicles, and more particularly to a combined safety vent and siphon unloading nozzle for railroad tank cars.
Liquid being transported in a vehicle may surge toward its end when the vehicle starts, stops or changes direction or speed suddenly. The surging liquid may locally trap and compress gas in the vehicle and thus cause a localized transient increase in pressure (e.g. 120 p.s.i. for 2.5 mili-seconds); the pressure quickly returns to normal as the surge subsides. Such vehicles frequently have safety vents with frangible discs for relieving excess pressure. It is highly undesirable for such discs to be broken by normal transient pressure surges because the broken disc must be replaced immediately or else the liquid will leak from the vehicle or become contaminated. Surge chambers have been used in conjunction with frangible discs for dissipating transient pressure surges without breaking the discs. However, such prior surge chambers have required single-purpose nozzles for communicating with the vehicle interior, and have increased the number of protrusions on such vehicles. Also, such prior surge chambers are often difficult to clean or line with a corrosion resistant coating.
Accordingly, it is an object of this invention to provide an improved transient pressure surge chamber for vehicles which transport liquids.
Another object is to provide a multi-purpose nozzle for railroad tank cars.
Another object is to provide a vehicle with a siphon unloading nozzle that serves the additional function of being the surge chamber for preventing premature rupture of a frangible element safety vent.
Another object is to reduce the number of holes through and protrusions from the skin of a railroad tank car.
Another object is to provide a safety vent surge chamber which is readily accessible for cleaning and lining.
Another object is to provide a railroad tank car combined siphon unloading and safety vent nozzle which is rugged, durable, relatively low cost, easily maintained, and which does not possess defects found in similar prior art devices.
Other objects and advantages of the invention will be found in the specification and claims, and the scope of the invention will be pointed out in the claims.